**Core Concept**
Osteoporosis is a metabolic bone disease characterized by a decrease in bone mass and density, leading to an increased risk of fractures. It is often associated with hormonal imbalances, decreased calcium absorption, and altered bone remodeling.

**Why the Correct Answer is Right**
Osteoporosis is indeed seen in all the mentioned conditions. Thyrotoxicosis, a condition of excess thyroid hormone, can lead to increased bone turnover and resorption, resulting in osteoporosis. Cushing's disease, caused by excess cortisol, also promotes bone resorption and decreases bone formation, contributing to osteoporosis. Menopause, characterized by the decline in estrogen levels, disrupts the balance between bone resorption and formation, leading to osteoporosis. The pathophysiology of these conditions involves the activation of osteoclasts, the cells responsible for bone resorption, and the inhibition of osteoblasts, the cells responsible for bone formation.

**Why Each Wrong Option is Incorrect**
**Option A:** Thyrotoxicosis primarily causes bone resorption due to the increased activity of osteoclasts, but it is not the only condition associated with osteoporosis.

**Option B:** Cushing's disease is another condition that contributes to osteoporosis by promoting bone resorption and inhibiting bone formation.

**Option C:** Menopause is also a significant risk factor for osteoporosis due to the decline in estrogen levels, which disrupts the balance between bone resorption and formation.

**Clinical Pearl / High-Yield Fact**
It is essential to note that osteoporosis can be prevented or treated with hormone replacement therapy (HRT) in postmenopausal women and with bisphosphonates in patients with thyrotoxicosis or Cushing's disease.

**✓ Correct Answer: D. All of the above**